1. Field of the Invention
The present invention relates to an apparatus for intermitting a beam bundle such as a sample beam bundle and a reference beam bundle in a gas analyzer such as a nondispersive infrared gas analyzer.
2. Description of the Prior Art
An apparatus for intermitting beams of light for use in a gas analyzer A, in which two ball bearings 10, 11 support a rotary shaft 9 of a chopper 2, as shown in FIG. 9, has been known. 10a, 11a designate outside rings fixedly mounted on a bearing housing 12 by means of adhesives and the like. 10b, 11b designate inside rings, both the inside rings 10b, 11b being prevented from moving axially outward relative to the rotary shaft 9 by a larger-diameter portion 9a of the rotary shaft 9, a fixing spacer 13 and a fixing ring 14.
For example, in an infrared gas analyzer, in general a quantity of a beam of light incident upon a sample cell and that incident upon a reference cell are balanced, an alternative electric signal being taken out by intermitting the beam bundle by a chopper, and the alternative electric signal being converted into a gas-concentration signal. In this case, if a bearing of the chopper has any play in the thrust direction or the radial direction, this play appears in the form of shake x of a shaft of the chopper 1, as shown in FIG. 10, and as a result, a difference is produced between the quantity of a beam of light incident upon the cell 3 and that incident upon the cell 4 and becomes a noise which reduces measuring accuracy. Accordingly, a precision ball bearing has been used for said ball bearings 10, 11 in many cases. However, even in this case, there is a clearance of several microns between outside rings as well as inside rings and balls 10c, 11c. This minute clearance leads to a shake of a shaft of the chopper 2 which leads to a noise.